Radio receiving system



April 26, 1932.

G. R. FISHER RADIO RECEIVTNG SYSTEM Filed Dec. 5. 1928 INVENTOR ByCQ/harn 6. Fisher A TTORNE Y5.

Patented Apr. 26 1932 UNITED STATES PATENT OFFICE GERHARD R. FISHER, OFPALO ALTO, CALIFORNIA, ASSIGNOR TO FEDERAL TELEGRAPH COMPANY, OFFRANCISCO, CALIFORNIA, CORPORATION OF CALIFORNIA RADIO RECEIVING SYSTEMApplication filed December 5, 1928. Serial No. 824,004.

This invention relates enerallyto systems for receiving radio signa s,and particularly to systems of this kind having means for minimizingstatic disturbances.

It is an object of this invention to devise a radio system incorporatingstatic eliminating means, which utilizes a mm mum of apparatus and iscomparatively s1mp1e to operate.

It is a further object of this invention to devise a radio receivingsystem which is comparatively free from interference due to potentialstatic.

It is a further object of this invention to devise means in conjunctionwith a loop an-. tenna which can be employed for eliminatlng staticinterference and also for imparting unidirectional characteristics tothe system.

It is a further object of this invention to devise a novel method ofoperating a radio system utilizing a receiver coupled to a plurality ofantennas.

Further objects of the invent1on W111 appear from the followingdescription in wh ch I have set forth the preferred embodiment of myinvention. It is to be understood that the appended claims are to beaccorded a range of equivalents consistent with the state of the priorart.

Referring to the drawings:

Fi re 1 is a diagrammatic view illustrating t e radio antennas utilizedin my system connected to receiving apparatus.

Fig. 2 is a circuit diagram illustrating one form of the system of myinvention.

The system of my invention utilizes in general a plurality of separateantennas or antenna portions which are connected to common radioreceiving means. Thus referrmg to Fig. 1 I have shown antennas-11 and 12connected to common radio receiving means 13. While these antennas maybe of any form which will secure the objects of the invention, I preferthat they both be of loop form as for example a plurality of-loops ofwire wound upon a suitable frame as shown. The plane of each loop isgenerally normally positioned vertically and the frames are mounted soas to be readily rotatable about a vertical axis. In some instances itis desirable to provide for adjustment of bothloo s about a horizontalaxis, as for example w enit is desired to take'in account reflectedradio signal or static energy. However such adjustment or positioning ofthe planes of one or both of the loops at an angle to the verticalposition shown is generally unnecessary exce t for energy of short wavelengths.

eferring to the circuit diagram of Fig. 2, loop antenna 11 is showntunable by suit able means such as a variable condenser 14 and iscoupled to' the radio receiver 16 by means of a suitable wave filter17.- Wave filter or coupling means 17 preferably is constructed so thatthe coupling between loop 11 and the receiver 16 can be varied asdesired. The filter which I have shown gives good re sults and consistsof a balancing condenser 19, in this case formed by relativelystationary electrodes 21 connected to the terminals of loop 11, and acentral electrode 22. The center electrode 22 is connected to oneterminal of an inductance coil 18. Another re active balancing device 23has its fixed electrodes connected to the terminals of inductance coil18, and has its center electrode con nected to one terminal of anotherinductance 24:. The other terminal of coil 24 has a ground connection26, and this inductance can be tuned as by means of variable condenser27. For transferring energy to the receiver 16 inductance 24 is showncoupled to a secondary inductance 28. Inductance coil 18 is preferablydivided into two portions by having its center tap connected to groundas indicated at 29.

Antenna 12 is also shown provided with a variable condenser 31 shuntedacross its terminals, altho in practice this antenna is detuned withrespect to the signal energy to be received. As a convenient means forcoupling antenna 12 to" the remainder of the apparatus I have shown acondenser 32 havm its one terminal connected to one termi-- 11a of loop12, and its other terminal connected to one terminal of inductance coil18. In series with condenser 31 I have sh own variable reactive meansformed by variable condenser 32, and phase shifting means formed by anad-" justable or variable resistance 33. The connection established bycondenser 31 in efiect couples loop 12 to one portion of the mductancecoil 18.

To secure certain advanta es to be later explained, I prefer to grounthe electrical center of loop 11, as by means ofa ground conductor 36connected to the center point of loop 11. L00 antenna 12 is likewisepreferably grounde in a similar manner b means of a ground conductor 37connecte to the center point of loop 12. Phase shifting 11. It has beenfound that this static energy can be divided roughly into two groups,one kind originatin at a remote point and having an a preambledirectional effect, and another kind which ma be termed potential staticwhich is cause by different potentials existing at various stratas abovethe earth. It isapparent that static having a directional effect atright angles to the plane of loop 11, will not be absorbed bythisantenna due to its figure ei ht characteristic. However whenreceived rom other directions such static will produce appreciableinterference if not neutralized or cancelled. Loop 12 is arranged insuch a positionv that it will receive such interfering directionalstaticzand the energy so absorbed is impressed upon the wave filter orcoupling means 17 together with the energy absorbed by antenna 11. Theintensity of impulses impressed upon coil 18 by loop 12 can be adjustedby varying the condenser 32, and the phase relationship can be adjustedby varying resistance 33. When the system is properly adjusted impulsesdue to static impressed upon coil 18 by antenna 11 are of substantiallythe same intensity and are substantially 180 degrees out of phasewith'the corresponding impulses from antenna 12. Thus such impulsesare'cancelled out or neutralized and ha e substantially no 'efiect uponthe receiver 16. l

The ground connections 36 and 37 for the loop antennas 11 and 12 aredesirable in that they minimize the effect of potential static upon thesystem. As previously explained such static is largely due to thepresence of different potentials occurring at difierent strata above theearth, such potential differences causing potential discharges thru theantennas. By utilizing loops grounded at their center points suchdischarges are in part directly conducted to ground and the efiect uponthe system is minimized.

Generally in the operation of my system reception is bi-lateral inaccordance with the directional characteristics of the loop antenna 11.It is possible however to modify the system so that the directionalcharacteristics correspond to a cardioid. It will be noted that inaddition to the circulatory loop currents in antenna 12 caused byabsorption of static energy, this loop also has a capacitative effectand can therefore be employed as an aperiodic capacitative antenna forabsorbingsignal energy. By properly adjusting the phase relationship ofsuch signal energy, as by cuttingin and varying resistance 38, signalenergy impressed upon inductance coil 18 from loop 12 can be madesubstantially in phase with the signal energy impressed upon the coilfrom main antenna 11. When this condition exists and proper coupling isprovided between loop 12 and inductance coil 18, the directionalcharacteristics of the sys-' tem'will be substantially a cardioid, orthe system will be unidirectional.

In practice I have found it desirable to have the loops 11 and 12arranged at substantially the same height from the surface of the groundand of substantially the same size. The ground connections are alsopreferably made to the upper sides of the loops as shown. Best resultsare secured by maintaining an angular relation between the planes ofloops 11 and 12, although this angular relation is generally somewhatless than 90 degrees.- The antennas can be placed any desired distanceapart or can be comparatively close together.

- Iclaim:

1. In a radio receiving system, a tuned loop antenna, means forgrounding the center point of said loop, a receiver, means for couplingsaid antenna to the receiver, said last means including a coil havingits center point grounded whereby it is divided into two portions, asecond loop antenna, means for grounding the center point of said secondantenna, said second antenna having its plane arranged at an angle tothe plane of the first antenna, phase shifting means associated with thesecond antenna and means for coupling said second antenna across oneportion of said coil.

2. In a radio receiving m, two antennas adapted to be afiected todifferent degrees by desired and undesired radio waves proceeding fromdifierent directions, a closed oscillatory circuit comprising aninductance having a mid-point tap and a three-plate balancing condenser,one of said antennas being connected across one half of said tappedinductance, the other of said antennas bein connected across the otherhalf of said inductance, and a receiving device connected between themid-point tap on said inductance and the third place of vsaid balancingcondenser. i

In testimony whereof, I have hereunto set my hand.

GERHARD R. FISHER.

